This invention generally relates to fluid transfer conduits (generally steel-walled, and single-walled) that are suspended between two work platforms. Examples of such work platforms include production platforms and drilling platforms (whether floating or weighted to a marine floor, or otherwise), floating service vessels (e.g. FPSOs), and other work platforms that will occur to those of skill in the art. Such conduits are typically referred to as xe2x80x9ccatenaryxe2x80x9d fluid transfer conduits. The invention also relates to systems and methods for prevention of clashing between multiple conduits spaced closely together and to methods of installation of multiple conduits at the same time.
Referring now to FIG. 1, a platform 1 is seen being serviced by floating vessel 2. Platform 1 is held in place by mooring 3, and floating vessel 2 is held by mooring 4 connected to turret 5. Connected between turret 5 and platform 1 are catenary conduits 6a-6c for transfer of fluids between platform 1 and floating vessel 2. Thermal expansion and other phenomena (e.g. internal pressure fluctuations) cause catenary conduits 6a-6c to move relative to each other. If made the same length, they would be too close together in the middle area between platform 1 and vessel 2 and would clash. Therefore, catenary conduits 6a-6c have different lengthsxe2x80x94to prevent them from clashing. Since they are different lengths, however, there are problems.
For example, using different lengths for transfer conduits means that only one transfer conduit is of an optimum length for the particular installation. The additional length of the other transfer conduits, needed to avoid clashing, costs extra money in materials, manufacturing time, installation, towing loads, etc. Therefore, there is a need for a multiple transfer conduit system having transfer conduits of substantially the same length.
Also, each of catenary conduits 6a-6c must be towed individually to the location where platform 1 has been moored. The use of multiple vessels for towing the catenary conduits and the production downtime during the installation of each individual catenary conduit 6a-6c is expensive. Thus, there is also a need for a conduit system between two work platforms that allows for the installation of, and towing of, multiple catenary conduits at one time.
One proposed system for addressing this problem is to use xe2x80x9cflexiblexe2x80x9d conduits. Such conduits are made of multiple layers and are extremely expensive to fabricate. However, due to their particular thermal-expansion qualities, which are much less than the thermal-expansion qualities of the steel pipe catenary conduits illustrated in FIG. 1, flexible conduits can be rigidly clamped together in the middle section between platform 1 and floating vessel 2. Thus, the flexible conduits are made substantially the same length. However, as mentioned before, flexible conduits are more expensive.
Thus, there is a continuing, long-felt need, for a system of steel catenary conduits between a production platform and service vessel in which the transfer conduits having high expansion properties are substantially the same length but do not clash.
Problems described above are addressed by various embodiments of the invention. Common to all embodiments is the separation of transfer conduits while allowing relative motion between them.
According to one aspect of the invention, an apparatus is provided for separating at least two transfer conduits connected between at least two work platforms while allowing for relative motion between the at least two transfer conduits. The apparatus comprises: a first transfer conduit engagement member, a second transfer conduit engagement member, and a separation member between the first and the second transfer conduit engagement members. The separation member allows for relative motion between the first transfer conduit engagement member and the second transfer conduit engagement member while maintaining a minimum distance between the first transfer conduit engagement member and the second transfer conduit engagement member.
According to a more specific example embodiment, the first and second transfer conduit engagement members comprise curved members having inner surfaces arranged for frictional engagement with the first and second transfer conduits, respectively. In some examples, the curved members comprise multi-piece clamps for substantially surrounding the transfer conduits. In another specific embodiment, for use with a third transfer conduit, a third engagement member and a separation member are provided between first and third transfer conduit engagement members.
According to a further aspect of the invention, an apparatus is provided comprising: a means for separating at least two transfer conduits and a means for allowing relative motion between the at least two transfer conduits. In one specific example embodiment, the means for separating comprises a substantially inflexible separation member pivotally connected to at least one of the transfer conduits (for example, through a first collar substantially surrounding a first of the at least two transfer conduits and through a second collar substantially surrounding a second of the at least two transfer conduits). In a further example, there is provided a means for separating a further transfer conduit connected between the at least two work platforms from the at least two transfer conduits.
According to yet another aspect of the invention, a work platform transfer conduit bundle is provided. In this aspect, the bundle comprises at least two transfer conduits, wherein at least one of the at least two transfer conduits comprises a material having a total expansion coefficient (contributed to by, e.g., thermal expansion and internal pressure) sufficient to clash with the other of the transfer conduits at a spacing of the transfer conduits in the bundle, means for separating the at least two transfer conduits, and means for allowing relative motion between the at least two transfer conduits.
In a specific example, means for towing the at least two transfer conduits is also provided (for example, a clamp holding a first end of the at least two transfer conduits). In some examples, the clamp comprises a substantially inflexible clamp and a tow-line receptacle (e.g. a padeye).
In some examples, the means for allowing relative motion between the at least two transfer conduits comprises a substantially rigid separation member pivotally attached to the at least one of the at least two transfer conduits.
According to a further embodiment, buoyancy means (a volume having a density less than water) is attached to the means for separating the at least two transfer conduits. Some examples use a housing entrapping a gas (e.g., a steel can, composite cylinder or other shape, plastic housing, etc.). Other examples use a material in solid phase wherein the material has a density less than water (e.g, urethane, foam, etc.).
In still a further example embodiment of the invention, a tie-down is provided for the buoyancy means, wherein the tie-down holds the buoyancy means in a fixed spacing to the transfer conduits. In as more specific example, a means is provided for holding the buoyancy means in a spaced relation to the transfer conduits (for example, a substantially inflexible line, such as a wire rope or strap) surrounding the buoyancy means and the transfer conduits.
In an even further example embodiment, a separator is provided between the buoyancy means and the transfer conduits, and further separators are between the transfer conduits.
According to yet another aspect of the invention, a method is provided for installation of transfer conduits between a pair of work platforms. The method comprises: towing a bundle of transfer conduits to the work platforms, wherein at least one of the at least two transfer conduits comprises a material having a total expansion coefficient sufficient to clash with the other of the transfer conduits at a spacing of the transfer conduits in the bundle, separating the at least two transfer conduits, and allowing relative motion between the at least two transfer conduits, connecting a first end of a first transfer conduit of the bundle to a first of the pair of work platforms. The method further comprises: connecting a second end of the first transfer conduit of the bundle to a second of the pair of work platforms, connecting a first end of a second transfer conduit of the bundle to the first of the pair of work platforms, and connecting a second end of the second transfer conduit of the bundle to the second of the pair of work platforms. In some embodiments, tow loads of the first end of the first transfer conduit and the second transfer conduit is transferred to a first work vessel in the same load transfer operation.